Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$142.90	12.268%	$160.431	$160.43	$160.45	$160.40
Purchase #2	$31.52	8.406%	$34.1696	$34.17	$34.15	$34.20
Purchase #3	$232.33	9.284%	$253.8995	$253.90	$253.90	$253.90
Purchase #4	$157.98	8.325%	$171.1318	$171.13	$171.15	$171.10
Purchase #5	$103.75	7.139%	$111.1567	$111.16	$111.15	$111.20
Purchase #6	$109.78	3.761%	$113.9088	$113.91	$113.90	$113.90
Purchase #7	$156.64	12.479%	$176.1871	$176.19	$176.20	$176.20
7 purchase totals =	$934.90		$1,020.8845	$1,020.89	$1,020.90	$1,020.90